Catalyst-Free Thermal Evaporation Synthesis of TiO<sub>2</sub> Nanostructures in Atmospheric Air

Abstract

TiO<sub>2</sub> nanostructures were synthesized using a thermal evaporation method without a catalyst. TiO powders mixed with graphite powders were used as the source materials. The synthesis process was performed in air atmosphere at 1000 °C. When the mass ratio of TiO/graphite in the source material was 2:1, TiO<sub>2</sub> nanowires and nanobelts started to form. As the mass ratio of graphite to TiO increased to 1:1, TiO<sub>2</sub> nanowires and nanobelts were formed in large quantity. The nanowires had an average diameter of 80 nm and lengths in the range of 3 ~ 11 µm. The average width and length of the nanobelts were 500 nm and 3.4 µm, respectively. However, with further increase in the mass ratio of TiO/graphite to 1:2, no nanostructures were observed. The mass ratio of graphite to TiO in the source material had an important effect on the formation of the TiO<sub>2</sub> nanowires and nanobelts. The X-ray diffraction data confirmed that the TiO<sub>2</sub> nanostructures had a rutile crystal structure. Two emission bands centered at 410 nm and 510 nm were observed in the room temperature cathodoluminescence spectrum of the TiO<sub>2</sub> nanostructures. The emission at 410 nm is attributed to the electron transition from the conduction band to the valence band in rutile TiO<sub>2</sub> crystal, which is indicative of the high crystallinity of the TiO<sub>2</sub> nanostructures.